Hydrofoils



y 1964 R. LOPEZ 3,132,619

HYDROFOILS Filed May 2, 1960 2 Sheets- Sheet 1 6 INVENTOR.

mm W

BY wsmxw,

ATTORNEYS United States Patent 3,132,619 HYDROFOILS Robert Lopez, Williamsport, Pa., assignor to Aqua-Elite Hydrofoil Corporation, New York, N.Y., a corporation of New York Filed May 2, 1960, Ser. No. 26,217 14 Claims. (Cl. 114-66.5)

f This invention relates to boats equipped with hydro- One object of the invention is to provide an improved combination of hydrofoils with the hull of a boat to obtain efficient results with simpler and less expensive hydrofoil apparatus.

In accordance with one feature of the invention, the rear hydrofoil structure is located under the hull of the boat, and all, or a major part of it, is within the transverse width of the portion of the hull immediately above it; while transverse stability is obtained by having a wider spread of the forward hydrofoils.

Another object is to provide an improved mounting for hydrofoils on a boat hull for holding the foils in working position and for swinging the foils into an elevated position clear of the water. This improved mounting is provided with simple and effective means for changing the angle of attack of the hydrofoils.

Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.

In the drawing, forming a part hereof, in which like reference characters indicate corresponding parts in all the views;

FIGURE 1 is an end view of one of the hydrofoils of this invention;

FIGURE 2 is a side elevation of the hydrofoil shown in FIGURE 1;

FIGURE 3 is a top plan view of the hydrofoil shown in FIGURES 1 and 2;

FIGURE 4 is a diagrammatic side elevation of a boat equipped with hydrofoils in accordance with this invention;

FIGURE 5 is FIGURE 4;

FIGURE 6 is a front view of the boat shown in FIG- URES 4 and 5; and n FIGURE 7 is a greatly enlarged sectional view taken on the line 7-7 of FIGURE 4.

The hydrofoil shown in FIGURE 1 includes three parts which are preferably aluminum castings welded together. A foil section 1 provides the main lifting surface of the hydrofoil and has a chord-wise cross-sectional thickness distribution similar to that of an airfoil section but with the curvaturemodified so as to obtain smaller pressure gradients.

The hydrofoil includes also a secondary foil section or member 2, preferably of rectangular shape, and with a chord-wise cross section similar to that of the foil section 1. This secondary section 2 serves two purposes. One is to increase the lift at take-off (that is, during the lifting of the boat hull out of the water) by providing ad ditional surface for the hydrofoil and a surface with a higher angle of attack than that of the foil section 1.

The other purpose of the secondary section 2 is to create a flow condition over and about the foil section a top plan view of the boat shown in 1 to eliminate bubble formation. The problem presented by bubble formation will be considered more fully as the description proceeds. Both the secondary section 2 and the foil section 1 are connected to a strut 3 extending upwardly and connected to the hull of the boat. The cross section of the strut 3 is streamlined in the direction of travel of the boat so as to offer a minimum of drag during take-off.

The secondary section 2 is preferably made with a slight taper so that the section varies with the bending moment of the cantilever loading, though some slight bending of the secondary section occurs When the con tour is flat. The platform can also be made with a moderate camber having the concave surface facing downwardly.

The angle of attack of the secondary section 2 is preferably greater than that of the foil section 1, the difference in angle of attack being between 2 and 4.

As shown in FIGURE 3, the secondary section 2 extends across the entire width of the foil 1 along part of the length of the foil, the trailing edge of the secondary section being behind the leading edge of the portion of the foil below it.

FIGURES l and 2 show the location of the water line WL-Z when the hydrofoil is traveling at high speed. Under such conditions the upper portion of the foil is above the water level; and the secondary section 2 and strut 3 are entirely clear of the Water. It will be understood, however, that the water line is above the secondary section 2 when the boat is originally starting and the actual position of the zero-speed water line WL-l on the strut 3 depends upon the particular installation of the hydrofoil on the boat hull.

The upper portion of the foil section 1, indicated by the reference character 5, is inclined at a dihedral angle of about 40 to the horizontal; but the lower portion of the foil section 1, designated by reference character 6, is at a lesser dihedral angle, preferably about 18. The reason for this difference in dihedral angle is to minimize the lift loss caused by the slope of the foil section 1.

There are three principal reasons for sloping the foil section 1 with respect to the horizontal; that is, for using dihedral angles. One is that in the event of bubble formation along the hydrofoil, the bubble will not spread to the full area of the hydrofoil. Another is that control of the direction of the boat is facilitated by the horizontal angles of the hydrofoil lift surfaces; and the third and principal reason for using the dihedral angle is to obtain a gradual change in lift with variation in the immersion of the hydrofoil. i

It will be evident that the greater the dihedral angle, that is, the nearer the lift portions of the hydrofoil ap proach the vertical, the smaller the lift-to-drag ratio becomes. For this reason, the dihedral angle is made smaller at the lower portion of the hydrofoil where adequate depth for safe operation has been reached. The platform of the main lifting surface, that is, the surfaces of the lower portion 6 of the hydrofoil, is tapered so as to increase the lift at a faster rate as the hydrofoil is submerged. The lower portion 6 is also swept back and this has been found highly desirable by experience.

In the description of this invention a hydrofoil as considered to be swept bac f if the leading edge slopes downward with a rearward component of extent, and

conversely, a hydrofoil is considered to be swept forward if the leading edge slopes downward with a forward component of extent. The expression swept back and swept forward are not used herein in connection with foils that have no vertical component of slope to the leading edge.

One advantage of the sweep-back is that grass or leaves or other objects suspended in the Water will slide along the leading edge of the hydrofoil and. off the tip so as not to effect the flow of water on the lifting surfaces when the boat is operating at moderate or high speed. Another advantage is that in the event of a collision with a floating log or other object, or even a collision with a fixed object in the water, the blow is always a glancing one.

Another advantages of the sweep-back is the obtaining of higher velocities without cavitation. The cavitation phenomena depends upon speed, pressure and temperature, and is a condition under which parts of the hydrofoil become subject to water vapor pressure while other parts are subject to direct pressure from the water itself. It is important, for satisfactory operation of the hydrofoils, to maintain direct contact of the hydrofoil surfaces with the water flow whenever the surfaces are submerged.

Another, and very important, advantage of the sweepback is its use with cantilever foils. It has been found advantageous to use foil sections which bend to some extent with variations in the load. This permits the hydrofoils to be made lighter, and it also results in a smoother ride when combined with sweepback.

The deflection of a cantilever hydrofoil under load changes the angle of attack. 'If the hydrofoil is swept forward, the load deflection increases the angle of attack, and this in turn, increases the load so that the deflection is still further increased and the load is again increased. Under such circumstances, the hydrofoil tends to climb out of the water and the operation becomes unstable.

By combining sweep-back with the cantilever hydrofoils of this invention, the deflection reduces the angle of attack with increase in load, and this causes the load on the hydrofoil to decrease. This result tends to stabilize the operation of the foils.

The secondary ection 2, when submerged, affects the flow of water over the lower portion 6 of the hydrofoil. When the boat is starting, and moving at low speed, grass or leaves that come in contact with the leading edge of the lower portion 6 do not slide off as easily as when the hydrofoil is moving at high speed. Bubble areas from Where the grass or leaves are stuck on the hydrofoil and the reduced lift of the hydrofoil makes takes-off difficult if the hydrofoil is not equipped with the secondary section 2. During take-off, the propeller thrust creates a moment about the center of gravity of the boat which tends to lift the bow and thus increase the angle of attack of the hydrofoils. This effect is beneficial in that the lift co-efficient is correspondingly increased; but the increase in the angle of attack seems to increase the difficulty of shedding the grass or leaves which are. stuck on the leading edge of the hydrofoil. The presence of the secondary section 2 above and close to the lower portion 6 of the hydrofoil, as shown in FIGURE 1, creates an interference effect on the bubble area on the lower portion 6, eliminates the bubble, and causes the grass or leaves to be cast off more easily.

In the preferred construction of the invention, the distance of the secondary section above the lower portion 6 of the hydrofoil section 1 is between one-haif and two times the lifting surface chord of the hydrofoil at the region of the center of pressure of the hydrofoil.

Grass and similar material is not ordinarily a problem when the boat is operating at cruising speed or faster unless the leading edge of the hydrofoil has notches or nicks such as are sometimes caused by collision with hard objects. When such notches or nicks exist, pieces of grass or similar material sometimes becomes wedged in the nicks and produce bubble formation. This results in loss of lift and causes the affected side of the boat to drop lower. When substantial drop brings a portion of the platform 2 into the water, the flow over the surface of the lower portion 6 of the hydrofoil is atfectedand this will in most cases result in a shedding of the grass or other material caught on the hydrofoils, as previously explained. If the bubble can not be eliminated by the effect of the secondary section 2, the secondary section provides life for a smooth settling of the boat into the water and eliminates what might be a rough landing if the secondary section 2 were not present.

FIGURES 47 show the invention applied to an outboard motor boat. This boat has a hull 10 with a transom stern 12 to which an outboard motor 14 is attached in the conventional manner. The motor 14 preferably has a vertical shaft of extra length so that a propeller 16 at the lower end of the vertical drive shaft is lower in the water than in the case of ordinary outboard motors.

There are two forward hydrofoils attached to the bow of the hull 10, one on the starboard and the other on the port side. Each of these hydrofoils is constructed as in FIGURES 1-3 already described, and each hydrofoil has the upper end of its strut 3 attached to a block 22 (FIGURE 6) that is used to reinforce the hull at the region at which the hydrofoil is attached. The strut 3 is connected with the boat by a pivot 24 and by bracket means that can be rotated about a horizontal axis to change the angle of attack of the foil sections that extend into the water.

The apparatus for adjusting the forward hydro-foils 20 is not illustrated since its illustration is not necessary for a complete understanding of this invention. It is described fully in my co-pending application, Serial No. 17,669, filed March 25, 1960.

At each side of the stern 12 there is a bracket 26. A rear hydrofoil St has struts 32 connected to the bracket 26 by pivots 34. The rear hydrofoil 3t) swings about the pivots 34 from a working position, shown in full lines in FTGURE 4, to an elevated position, shown in dotted lines.

The rear hydrofoil 34 has a foil section with a chordwise cross section similar to the forward hydrofoils, except that in the preferred construction of the rear hydrofoil 5i there is no taper to the hydrofoil in a span-wise direction. The advantage of this uniform chord-wise dimension of the rear hydrofoil is that it permits the construction of the hydrofoil from an extruded section of metal, and this effects a substantial saving in cost. Since the rear hydrofoil 3th is not a cantilever foil, there is no necessity for a tapered section.

The rear hydrofoil 30 extends across the full width of the hull It in the construction illustrated, though a narrower foil can be used if the brackets 26 are located closer together. The center of the hydrofoil 30 is attached to the hull by a connector 4% The foil is symmetrical on both sides of this center structure; and each side has three different sections.

From its center, the hydrofoil 30 first slopes downwardly and rearwardly, this first section being indicated by the reference character 42. At the rearward end of this first section 42, on each side of the foil, there is a second and substantially level section 44, and there is a third section 46 that extends from the level section 44 upwardly and rearwardly to the strut 32 which connects the rear hydrofoil 3%) to the bracket 26. This hydrofoil construction can be made by merely bending an extrusion at the lines of juncture of the sections 42, 44 and 46; but at the middle of the foil it is usually necessary to attach separate extruded sections to the connector 40, preferably by welding so as to obtain an integral one-piece hydrofoil and connector 40.

The rear hydrofoil 30 is preferably equipped with secondary sections 2 attached to the struts 32 and serving a similar purpose to that of the secondary sections 2 of the forward hydrofoils 2i).

The connector 40 may be attached to the hull in various ways with provision for moving the connector up and down to change the angle of attack of the rear hydrofoil 30. In the construction. illustrated, the hull 10 is provided with a well 50 along the keel of the boat and similar in construction to a conventional centerboard well.

When this construction is used, the connector 40 is made long enough to extend upwardly through the well 50, as shown diagrammatically in FIGURE 7.

There is a handle 42 at the upper end of the connector 40 and extending beyond the top of the well 50. This handle can be used for raising and lowering the forward end of the rear hydrofoil 30 so as to change its angle of attack.

In order to hold the hydrofoil 30 at the desired angle of attack, the connector 40 is provided with means for locking it in various positions, FIGURE 7 shows a pin 54 which can be inserted in any one of various openings 56 through the sides of the well 50 above the water line. There are openings 58 through the connector 40 for receiving the pin 54. By having these openings 58 at somewhat different spacing from the openings 56, a fine degree of adjustment can be obtained for the connector 40. In connectionwith the broader aspects of the invention, the well 50 and the means for holding the connector 40 at various elevations is merely representative of adjustable means for connecting one end of the hydrofoil to the hull of the boat.

In the operation of the boat, the lift of the hydrofoils 20 and 30 raises the hull 10 clear of the water. The water line may be at the level indicated by the reference character WL-Z for a particular loading of the boat. Heavier loading will causethe hydrofoils to be immersed more deeply in order to provide the area necessary for additional lift, or the extra load may be compensated by increasing the angle of attack of the hydrofoils.

'For small boats, the hydrofoil 30, located under the boat, will not provide a high degree of stability; but combined with the forward hydrofoils 20, which have a wider spacing, this invention obtains ample stability.

Another advantage of the wide spacing of the forward hydrofoils and the centered location of the rear hydrofoil is that the water flow to the rear hydrofoil 30 is substantially undisturbed by the forward hydrofoils '20, especially in boats traveling at high speed and where the transverse wave travel from the forward foils is very small before the rear foil reaches the water adjacent to that through which the forward foils have passed.

The preferred embodiment of the invention has been illustrated and described, but changesand modifications can be made and some features can be used in different combinations without departing from the invention as defined in the claims.

What is claimed is:

1. A hydrofoil craft including a hull, two hydrofoils attached to the forward portion of the hull and extending below the level of the bottom of the hull and from both sides of the hull and for a substantial distance outward beyond the hull, the hydrofoils having portions that are submerged and portions that pierce the surface when the craft is foilborne and the submerged and surface-piercing portions having swept back leading edges, andhydrofoil means attached to the stern portion of the hull and with at least the major portion of said hydrofoil means located under the hull and within the limits of the transverse width of the hull, said hydrofoil means that are attached to the stern portion having part of the length of their leading edge swept back and another part of the length of their leading edge swept forward.

2. The hydrofoil craft described in claim 1, and in which the craft includes a propeller located in the water and there are hinge means at the stern of the boat attach ing the hydrofoil means to the hull, and on which the hydrofoil means swing between a working position rearward 6 of the propeller and a raised position cleaf of the dis placement water line of the hull.

3. The hydrofoil craft described in claim 2, and in which the hydrofoil means are continuous from one side of the hull to the other and of a generally W-shape when projected on a vertical plane extending transversely of the craft, and said hydrofoil means are pivotally attached to the hull at both sides and there are detachable fastening means intermediate the opposite sides of the hydrofoil means for connecting the transverse mid-portion of said hydrofoil means to the hull.

4. The hydrofoil craft described in claim 3, and in which the detachable fastening means are at the transverse center region of the hull and adjacent to the keel.

5. The hydrofoil craft described in claim 3, and in which the transverse mid-portion of said hydrofoil means is at the forward end thereof and the detachable fastening means includes an adjustable element operable to move the forward end of said hydrofoil means up and down to change the angle of attack of the hydrofoil means.

6. The hydrofoil craft described in claim 3, and in which the hydrofoil means are swept back from its center region that is above the foilborne water line of the craft, and the detachable fastening means connect with said hydrofoil means at the center region.

7. The hydrofoil craft described in claim 3, and in which the forward hydrofoils are pivotally connected to the hull and swing about fore-and-aft pivots to raise said forward hydrofoils above the displacement water line of the hull.

8. The combination with a boat hull of hydrofoil means, brackets connected with the hull at the stern thereof, pivot connections by which the hydrofoil means are attached to the brackets and on which the hydrofoil means swing from a working position under the hull to a raised position beyond the stern and above the displacement water line of the hull, the hydrofoil means having a center portion that is located under the keel line of the craft, and means connecting the hull and said center portion when said hydrofoil means are in their working posi tions.

9. The combination described in claim 8 and in which the hull has a center well opening through the bottom of the hull, and there is an extension of the hydrofoil means that extend up into the Well when the hydrofoil means are in working position.

10. The combination described in claim 9, and in which the connection includes detachable fastening means con- .necting the extension with a side of the well, and said fastening means are adjustable to raise and lower said extension to change the angle of attack of the hydrofoil means.

11. The combination described in claim 8, and in which the hull has a propeller in the water below the stern, and the hydrofoil means are continuous across the width of the hull, and the mid portion of said hydrofoil means are located in front of the propeller and at a level above the propeller when in working position, and the length of said hydrofoil means is so proportioned with respect to the pivot connections that the mid portion swings below and clears the propeller from moving from working position to a raised position astern of and above the level of the propeller.

12. In a hydrofoil craft, hydrofoil means comprising a foil section of uniform cross section throughout its transverse width and having an inner portion that extends downwardly and rearwardly at an acute angle to both the length and the width of the hull, a second portion that extends outwardly and more nearly horizontal than the first portion, and an outer portion that extends upwardly and rearwardly from the second portion and to a level above the foilborne water line of the craft.

13. The combination described in claim 12, and in which the hydrofoil means is of one piece construction and is symmetrical on both sides of a center connection which secures the hydrofoil to the hull, and pivotal connections at both ends of said hydrofoil means and on which the hydrofoil means are adapted to swing forward and aft.

14. The combination with a hydrofoil craft having a hull, of hydrofoil means, pivotal connections extending transversely from opposite sides of the hull and on which the hydrofoil means swing forward and aft, said hydrofoil means having a mid-portion with foil sections that extend upwardly toward the keel portion of the hull, and detachable fastening means connecting the mid portion of the hydrofoil means to the hull adjacent to the keel line of the hull, the leading edges of all portions of the hydrofoil means sloping rearwardly as they extend outwardly from the keel of the craft.

Clifton July 9, 1929 Hill Feb. 24, 1942 2,856,879 Baker Oct. 21, 1958 2,906,229 Boericke Sept. 29, 1959 2,984,197 Bader May 16, 1961 2,998,792 Hasler Sept. 5, 1961 5 FOREIGN PATENTS 458,807 France Aug. 18, 1913 529,476 Canada Aug. 21, 1956 19,496 Great Britain of 1907 10 582,985 Great Britain Dec. 4, 1946 657,438 Great Britain Sept. 19, 1951 814,173 Great Britain June 3, 1959 420,825 Italy May 6, 1947 129,628 Sweden Oct. 3, 19 50 15 OTHER REFERENCES Tietjens A. P. C. application, Ser. No. 268,421, published May 11, 1943.

Yachting, April 1958, vol. 103, No. 4, page 71 relied 20 on. 

1. A HYDROFOIL CRAFT INCLUDING A HULL, TWO HYDROFOILS ATTACHED TO THE FORWARD PORTION OF THE HULL AND EXTENDING BELOW THE LEVEL OF THE BOTTOM OF THE HULL AND FROM BOTH SIDES OF THE HULL AND FOR A SUBSTANTIAL DISTANCE OUTWARD BEYOND THE HULL, THE HYDROFOILS HAVING PORTIONS THAT ARE SUBMERGED AND PORTIONS THAT PIERCE THE SURFACE WHEN THE CRAFT IS FOILBORNE AND THE SUBMERGED AND SURFACE-PIERCING PORTIONS HAVING SWEPT BACK LEADING EDGES, AND HYDROFOIL MEANS ATTACHED TO THE STERN PORTION OF THE HULL AND WITH AT LEAST THE MAJOR PORTION OF SAID HYDROFOIL MEANS LO- 